Photographic type composition



y Jan. 23, 1962 R. C. OBRIEN PHOTOGRAPHIC TYPE COMPOSITION 2 Sheets-Sheet 1 Filed Deo. 4, 1959 INVENTOR.

RICHARD C. O'BRIEN ATTORNEYS /wS mm mg :maw V N" motz mwMll Ew (m QN Om mom- 3. mv HH. mm mm Eko f $20962 uw mk S. wwrotzm lmwo zQSzmwa wooo l. mozmzm fR /ww S SL Jan. 23, 1962 Filed Deo. 4, 1959 2 Sheets-Sheet 2 FIG -2 FROM PG so '7o 176 A P g DETECTOR` coNTRol. W68

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FIG-3 I PICA 2 PICA 4 PICA 8 PICA I6 PICA 32 PICA INVEN TOR. |2T BY RlcHARD c. oBRlEN MM,MM%

ATTORNEYS States Unite This application relates to photographic type composition, particularly to improved apparatus for tabulating with phototypesetting machines.

An important feature of this invention resides in the comparison of an analogue signal, in the form of a Variable voltage related to a desired spacing requirement, with another variable voltage or analogue signal indicative of the portion of space used in a line of predetermined length, for example as determined by the relative positions of the character image projecting and image recording parts of the machine. The invention contemplates the use of these signals particularly to supply actuating signals to operate certain spacing mechanism in the machine for indenting or the like as in tabulating.

In tabulating, a signal is provided corresponding to the distance between a given point in the line, i.e., the beginning or the end, and a desired position in the line, and this signal is compared with another signal corresponding to the actual position of the machine spacing mechanism during the composing or recording opera-tions. A nulling device is arranged to cause spacing movement in the machine until such time -as the two signals are equal and cancel each other. Thus, the photographing or character recording apparatus of the machine may be caused to assume a position spaced along the line from some reference point as desired.

The principal object of this invention is to provide tabulating mechanism for phototypesetting machines which enables the composer to advance the character spacing mechanism to preselected positions along the length of a line.

Another object is to provide such tabulating mechanism apparatus wherein an analogue signal is maintained co1'- responding to the instantaneous position of the character recording apparatus during composition of a line, and a tabulating location signal is provided and compared with the position signal to determine the locating of the recording appara-tus in a desired position for tabulating.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings- FIG. 1 is a schematic diagram of pho-totypesetting apparatus in accordance with the invention;

FIG. 2 is a schematic diagram of the Itabulating control provided by the invention;

FIG. 3 is a diagram of a component used in FIG. 2; and

FIG. 4 is a `diagram of a suitable phase and null detector for use in FIG. 2.

Referring to the drawings, which illustrate a preferred embodiment o-f the present invention, FIG. 1 is a schematic representation of a high speed phototypesetting apparatus including a rotating matrix disk carrying the characters to be reproduced as, for example, transparent portions in a significant zone of predetermined radial depth on the disk. The character zone is represented in FIG. l by the character A. In other zones of the disk there are a series of timing ymarks 12, one for each character on the disk, and in a further zone there is a single reference mark 13 the purpose of which is to supply a starting pulse. In another zone a binary space code related to and identifying the relative width of each character is supplied in the form of a series of transparent atent O fice dots 15 on the disk, shown for purposes of illustration as representing a five digit binary code. It will be apparent, of course, that the marks, dots, and characters on the disk may be either transparent or opaque, so long as they contrast with the background area of the disk.

The overall arrangement of the apparatus may be generally similar to that disclosed in Patent 2,846,932 or copending application Serial No. 640,741, filed February 18, 1957, now Patent No. 2,944,472, issued July 12, 1960, both of which are assigned to the assignee of this application, although the invention is also useful with similar machines, wherein a punched tape record is prepared by keyboard operation and utilized to control the photographic oper-ations.

In general, the arrangement of the apparatus is as follows. A flashing light source of high intensity and short duration is provided, such as by the spark gap 20 controlled by the spark control unit 22, and this light source is arranged to illuminate the character zone of the disk through a lens 23, with the resulting image bearing light beam being focused through a lens system 25 upon a record film strip 28 which is supported across the light beam between film drum-s 29. The character image bearing light beam passing to lm strip 28 is intercepted by a space prism system 30 controlled by a suitable transducer 32 for displacing the light beam with respect to the film strip without altering the focus thereof.

A further flashing light source 35 connected to a space control unit 36 is arranged to illuminate the space code dots 15 through a lens 37, and the resulting one or more small light beams passing through the disk fall upon a bank of photocells 40 which provide a space code pickup.

The information from the space code pickup is supplied to a space memory computer 42, this information being used to preset the later stages ofthe binary counter as disclosed in detail in said Patent 2,846,932. The remaining or rst stages of the space memory computer are preset by a suitable point set control 44, so that the output through line 45 represents the product of the preset and the required space for the illuminated character as transmitted from the space code pickup 40.

lamp 50 and lens 51 direct a light beam through the zone of timing marks 12, the resulting pulsating light lbeam falling upon the photocell 52. The pulsating output of this photocell is directed through an amplifier 53 and through a delay circuit 54 into a selector counter 55, as described in detail in said copending application Serial No. 640,741. A further lamp 57 and lens 58 direct a light beam through the zone of the index mark 13, and the resulting light beam falls upon the photocell 60 once during each rotation of the disk 10, thereby providing an index from which the location of any selected character on the disk may be determined by counting the number of timing pulses occurring after the index pulse. The outputof photocell 60 is connected through amplifier 62 to selector counter 55, and is arranged to reset the counter to a zero count to provide the desired index or reference point. The count in the selector counter 55 is, then, indicative of the position of each character on disk 10 with reference to the index mark 13.

A suitable keyboard, such for example as the keyboard 65 of a typewriter, is arranged to actuate a bank of permutation switches or the like indicated schematically at 66, and these switches are arranged to provide binary code information identifying the selected character to a suitable code storage 68. The information in code storage 68 is supplied through its output 60 to a coincidence circuit 70, and the output 71 of selector counter 55 is likewise received in the coincidence circuit. Thus, when the code information in code storage 68 corresponds to the count of selector counter 55, an output signal will be transmitted through the coincidence output 72 to a suitable gate circuit 75, as more fully explained in said copending application Serial No. 640,741.

Gate circuit 75 also receives undelayed timing pulses directly from amplifier 53 through line 76, and thus when an output signal passes through coincidence output 72, the output line 78 of the gate circuit will transmit a trigger pulse on the next received timing pulse from line 76. The trigger pulse is supplied to a pulse generator 80 for the purpose of starting the same, and the trigger pulse also is transmitted through line 82 to the spark control unit 22 and space control unit 36 for flashing the light source and 35, respectively. This causes the light source 20 to illuminate the selected character and the resultant character image is recorded on lilmstrip 28. At the same time, space code information is supplied to the pickup apparatus 40'and is used to set up the space memory computer 42, the point set control having been set manually to arrange for the desired sizeof type set.

The pulse generator 80 has its output 85 connected toa space memory counter'v88, and line 85 is also connected through la line 89 to the spacememory computer 42. The output line 45 ofthe lspace memory computer is in turn connected back to'pulsegenerator 80 to supply a stop pulse thereto, and thus after the space memory computer has counted a number of output pulses from generator 80 equalto the product ofthe point set and the space requirement of the selected characterimage, the pulse generator 80'is stopped. As a result of this the number of pulses transmitted `to space memory counter 88 is a digital representation of the space required for the selected character at the desired point setting.

Space' memory counter 88 is'a multistage cascade com nected binary counter, one embodiment of the invention having used a thirteen stage counter for this purpose. The yiirst'seven stages of` this counter `are connected to' theprism spacing transducer'32 through the output coni nection 90, and the eighth stage'of counter'88 `is connected through an output line 92 to a lilm advance'tra'nsducer 93 which controls rotation of one of the -flm reels 29 to advance the film ystrip 28 with respect to-the image bearing light beam through'predetermined large space increments.

As more fully explained in copending application Serial No. 661,633, led May 27, 1957, now Patent No. 2,966,-

835, the arrangement of thev parts in such that one pulse fed into space rmemory counter 88 is equal to one 17128 of a pica, and this smalll discrete space measurement is referred to hereinafter as a space unit ora piclet. Therefore, the rst seven stages of space memory counter 88 handle spacing requirements from 1/128 to 127/128 of a pica and transmit this spacing information through Voutput 90 to the prism controlling transducer 32. Movement of the spacing prismsystem 30 thus controls all spacing requirements up to "one'space unit less than a full pica.

The output line 92@ transmits a pulse to the tilm advance-transducer 93 only when the spacing requirements equal or exceed a full pica, yand the arrangement of this transducer isfsuch (as explained in said copending application Serial No. 661,633), that for every pulseV received through line 92 the ilm strip is advanced through a distance of one pica and the prism system is readjusted accordingly. The advance portion of the film strip is held stationary during the composingl of a single line by the index-punch, indicated generally at 94, and when the spacing movement of strip 28 is complete for one line this punch -is releasedk and the film` advanced into the takeup reel, as more fully explained in said copending application.

The capacity of space memory counter 88 is preset by "a suitable line length control 95 so that when the counter 88 fillsup an end of line sequence (includingV release of punch 94)v can be ,initiated in' any kwell known mannen In practice' a lthirteen stage binary/counter has counted and the maximum available space for a linef will be the space which must be divided between the wordspaces in the line to justify.

Spaces between words, hereinafter referred to as Word spaces, are inserted in uniform length in this apparatus, and these spaces later are adjusted in suitable justifying apparatus operating from the film strip 28, as more fully explained in said Patent 2,846,932. Thus, whenever the word space bar `100 on the keyboard is actuated a pulse is fed through line 102 to a word space memory counter 105, and such pulse also is passed .through line 106 to the lm advance transducer 93, causing the film strip to be advanced through a suitable word spacing movement. Counter is a further binary count-e1', illustrated as a live stage counter. lts output 108 extends to a suitable code lamp panel 110 arranged adjacent the film strip 28, and a further output 112 from space memory counter 88 also extends to panel 110. The purpose of this arrangement is to provide a scoreboard which indi-` cates, in suitable binary code, the total space unused in each line, and the total number of word spaces in the line, from counter 105. At the end of each line the code on panel 110 `is projected onto `the lilm strip to provide the permanent `record of this information thereon as a series of code dots.

As noted previously, the space memory counter 88 is: preset for a predetermined line length, and thus the: count at any given time in the counter is indicative of' the tot-al space used, and the complement of this to-tal is; the space remaining in the line. The word space memory counter 105 totals the word` spaces used, andv this infor-V mation from counter 105 is recorded'` on the film at theI end of composition ofl each line, to be used to compute justifying space in a later operation. Referring to FIG.. 2 the connection between space memory counter 88 andf its output 92 is shown as including an amplifier 115 con-- nected to receive output pulses from the seventh counter 88 and passl it on to the transducer' 93, with each sucl11 pulse having a spacing value of one pica,

In accordance with the invention, a following counter 117lhaving six binary stages corresponding to the eightlr through thirteenth stages of counter 88, also receives the: output pulses from the seventh stage of 88, and its sixi stages are connected through the amplifiers 119-124 tot contro1,'individually, six single pole double throw relays 12S-130. These relays control the tapped secondary oft a transformer 135, the primary Winding of which is con-- nected to a suitable source 136 of constant A C. Voltage.. As is apparent from the drawing, when one or more of the relays 12S-130 is energized more or less of the secondary windings of transformer vare connected in the: circuit between the line 140 and ground.

Recalling that counter 88 is preset for a predetermined' line length, and that as pulses are supplied to this coun-- ter they tend to fill up the counter to its preset capacity,. therefore the count fed into the counter will represent; the instantaneous position of the character recordingi equipment, and the complement of the count equals ther space remaining in the line. In the illustrated example the thirteen stage counter 88 has a capacity, for purposes of illustration, of 64 picas in increments of 1/128 of a pica. Therefore, the eighth stage (from the top in FIG.V 2) of counter 88 represents the one pica stage and a pulseinto this stage is indicative of a lilm advance vof one pica, as explained previously. The counter 117 'thereforemaintains a count o-f space used in pica increments.

Referring to FIG. 3, the transformer 135 may, for ex-V ample, have a primary winding with 1,920 turns and six secondary'windings of16,- 32, 64,` 128,256 and `512 turns,l

respectively. The first or 16 turn tap is controlled by a relay 125 which is connected to include the sixteen turns of this tap in the secondary winding or to shunt this tap out of the secondary, depending upon the position of relay 125. In a similar manner relays 126, 127, 128, 129 and 130 control the other five secondary windings as shown. With all of the relays -moved to the left or shunt position, as shown in FIG. 3, the potential between line 140 and ground will be zero, and assuming that the voltage impressed upon the primary winding of transformer 135 from the A.C. source 136 is 120i volts, then if relay 125 is caused to shift to include the sixteen turn Winding between ground and line 132, this output line will be at a potential of one volt.

It follows, therefore, that .the voltage derived from each of the individual windings controlled by the respective relays 126-130 will be 2, 4, 8, 16 and 32 volts, respectively, giving a total range of output voltage in line 140 of from zero to 63 volts in increments of one volt. Thus, if one pulse is received by the following or tabulator counter 177, relay 125 may be caused to shift corresponding to the change in state (as from zero to one) of the first stage of the counter and an output of one Volt will appear in line 140. Thus, each pulse received in counter 117 may be equivalent to one pica and produce an effective increase in the output line 140 of an additional one volt.

A multi-tapped potentiometer 155 is connected across the A.C. source 136, and this potentiometer is provided with uniformly spaced taps, the resistance between each of the taps being such that the potential difference between taps is one volt. These taps may be connected through suitable patch cords 156 to the successive contacts of a stepping switch S, and the common output line 160 of this stepping switch is connected to one side of the primary winding of a transformer 162, with the other side of the primary winding being connected to output line 141i. The stepping switch is controlled by a manually operated switch 163 which is operated by the tabulator key 165 on the compositors keyboard 65.

The secondary winding of transformer 162 is connected to a conventional detector circuit, indicated generally at 168, controlling a pulse generator 170 which will generate pulses whenever the potential of line 160 is greater than the potential of line 141i, but not vice versa. The output of the pulse generator passes through output line 172 which feeds pulses to tabulator counter 117 and `also to the one pica stage of space memory counter 38, and through line 92 to the transducer 93.

A suitable detector circuit (FIG. 4) may include a triede 175 having its grid and cathode connected to opposite sides of the secondary winding of transformer 162. Current flow in one direction only through the primary transformer winding will result in a positive voltage at the grid, causing the triode to conduct and producing a control voltage in line 176 to pulse generator 170. This may be arranged such that the generator operates only when the control voltage exists.

In operation, when the compositor presses tabulator key 165 he causes the step switch 15S to move to, for example, its rst position. The potential in line 160 will then be at some value indicative of the desired indentation or tabulation, in the ratio of one volt per pica. For example, assuming that two picas indentation is desired, the patch cord 156 from the first contact of step switch 15S is connected to that tap on potentiometer 155 from which a two volt output will be obtained. The secondary windings on transformer 135 are, at the beginning, all shunted out of circuit, the tabulator counter 117 being reset to zero at the beginning of a line. The voltage in line 14@ is therefore zero, and a potentialdifference of two volts exists in the primary of transformer 162, causing an induced voltage in the secondary of that transformer. The detector 168 and pulse generator 170 will provide output pulses whenever any flow of current in 6 this direction is detected in the secondary of transformer 162.

As will be seen from the above described example, the first pulse to the tabulator counter will cause relay to shift bringing the potential of output line up to one volt, but there is still a one volt potential difference across the primary of transformer 162, and pulses continue to pass through line 172. The next pulse, however, will drop relay 125 back to its normal position and shift relay 126 to connect the 32 turn secondary winding into the circuit, and at this time the potential of line 140 will step up to two volts, thus nullifying the two volt potential of line and causing the detector-pulse generator network to cease generating pulses. At the same time that these two pulses were fed to tabulator counter 117 they also passed to the one pica stage of space memory counter 88, and also caused operation of the spacing transducer 93 to advance film 28 two picas with respect to the optical axis. As the compositor continues, additional spacing pulses passing to the one pica stage of counter 88 will also be received by tabulator counter 117 causing the magnitude of the voltage in line 140 to increase in value correspond- `ing tothe position in the line at which the phototypesetter is then operating with respect to the beginning of the line. However, when the potential in line 140 exceeds that in reference line 160, the detector circuit 168 will not respond. If the compositor wishes to tabulate again he merely presses key 165, causing the stepping switch 158 to advance to its next position and a new reference voltage, higher than in line 140, is set up in line 160. The spacing mechanism is then caused to traverse, as explained above, until the potential in line 140 corresponds to and nulliiies the reference potential in line 160.

While the forms of apparatus herein described constitute embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A tabulating device for phototypesetting apparatus comprising means for producing a spacing control according to the spacing requirements of each character used during composition of a line, means producing a rst analogue signal varying with and related in magnitude to the space used while composing a line of given length, means for producing a second analogue signal related in magnitude to the space between the beginning of a line and a desired tabulating position in the line, means cornparing said signals and adapted to produce an output signal only when said first and second signals differ in magnitude, and a tabulation spacing connection between the output of said comparing means and said spacing control means operative to produce spacing control in accordance with said output signal with consequent change in the magnitude of said rst signal toward a coincidence with said second signal.

2. A tabulating device for phototypesetting apparatus comprising means for producing spacing movement according to the spacing requirements of each character used during composition of a line, means producing a rst analogue signal varying with and related in magnitude to the space used while composing a line of given length, means for producing a second variable analogue signal related in magnitude to the space between the beginning of a line and a desired tabulating position, means operable to vary the magnitude of said second signal to cor- Irespond to a desired position in a line to be composed, means operable to compare said signals and to produce an output signal only when said first and second signals differ in magnitude, and a tabulation spacing connection from the output of said comparing means feeding back to said spacing movement means for producing spacing movement in accordance with said output signal with consequent change in the magnitude of said first .signal toward a coincidence with said second signal.

3. A tabulating device for phototypesetting apparatus having mechanism for selecting variable width-characters in predetermined sequence to form aline of composition, said device comprising means producing spacing according to the spacing requirements of each character and each interword space used during composition of a line, means producing a iirst signal related in magnitude to the space used while composing a line of given length, means for producing a second variable signal related in magnitude to the space between the beginning of a line and a desired tabulating position in the line, means comparing said signals and producing a controlling output signal only when said tirst and second signals differ in magnitude, and a tabulation spacing connection between the output of said comparing means and said spacing means for causing spacing in accordance with said output signal with consequent change in the magnitude of said tirst signal toward a coincidence with said second signal.

4. A tabulating device for phototypesetting apparatus having a character selecting device adapted to select characters of predetermined width and form such characters into a line of composition, comprising means producing spacing of the characters according to their respective spacing requirements and interword spacing during composition of a line, means producing a `first signal related to the space used during composition of a line of given linal length, means for producing a second signal related in magnitude to the space between the beginning of the yline and a desired tabulating position, selectively operable means comparing said signals, a pulse generator controlled by said comparing means to produce output pulses only when said rst and second signals dier in magnitude, and a tabulation spacing connection between the output of said pulse generator and said spacing means for producing spacing in accordance with said output pulses with consequent change in the magnitude of said rst signal to coincide with said second signal.

5. In phototypesetting apparatus, aftabulating control,-

comprising means for accumulating the space used in composing a line of predetermined nal length, means producing spacing movement during composition of the line for locating each character including a transducer driven with said space accumulating means, means connected to said space accumulating means providing an analogue output signal related to the `instantaneous location of said spacing means in a line of composition, a tabulating device including means providing an analogue output signal representing a desired spacing from the beginning of the line,

andn selectively operable comparing means having an operating output connection to said transducer for comparing -said signals from said counting means and from said tabulating device, said comparing means being operative to effect spacing movement when there is an unbalance between said signals by actuating said transducer in a direction to change said location signal toward a value corresponding to the signal from said tabulating device.

6. In phototypesetting apparatus, a tabulating control comprising a counter for accumulating the space used in composing a line of predetermined final length, means producing spacing movement during composition of a line for locating each character including` a transducer driven with said counter, means connected to said spacing means providing an output signal related to the instantaneous location of said spacing means in a line of composition,

-a tabulating device including means providing a signal representing a desired spacing from the beginning of the line, comparing means operative to compare said signals from said counting means and from said tabulating device, and a pulse generator controlled by said comparing means and connected to etect spacing movement when there is an imbalance between said signals by actuating said transducer ina direction -to lchangesaid location signaltoward a value corresponding to the signal from said tabulating device.

7. In phototypesetting apparatus, a tabulating control comprising'a counter connected to accumulate counts representing the space used in composing a line of predetermined final length, means producing spacing movement during composition of a line for locating each'character including a transducer driven from said counter, means connected to said counter providing an output signal related to the instantaneous location of said spacing means in a line of composition, a tabulating device including means providing an output signal representing a desired spacing in the line, means connected to compare said signals, and a pulse generator controlled by said comparing means and operative to eiect spacing movement when there is an unbalance between said signals by supplying spacing pulses to said counter and said transducer to change said location signal toward a value corresponding to the signal from said tabulating device.

8. In phototypesetting apparatus, a tabulating control comprising means for determining the space used in composing. a line of predetermined final length, means producingv spacing movement during composition of a line for locating each character including a transducer driven from said determining means, means operable in correlation with said spacing means providing an output signal related to the instantaneous location of said spacing .means ina line of composition, a tabulating device including means providing a tabulating signal representing a desired spacing from the beginning of the line, and comparing means having an operating output connection to said transducer and said spacing means and connected -to compare said signals, said comparing means being operative to effect spacing movement when there is an unbalance between said signals by actuating said transducer to change said location signal toward a value corresponding to the signal from said tabulating device and to supply related spacing information to said space determining means.

9. A tabulating device for phototypesetting apparatus having character projecting mechanism and photosensitive material for recording the character images in sequence thereon, comprising means for producing spacing move- ;ment according to the spacing requirements of each character used during composition of a line between said projecting mechanism and said material, means producing a tirst analogue signal related in magnitude to the space used while composing a line of given length, means for producing a second analogue signal related in magnitude to the space between the beginning of a line and a desired tabulating position spaced from the beginning, means comparing said signals and adapted to produce an output signal only when said first and second signals differ in magnitude, and a tabulation spacing connection between the output of said comparing means and said spacing movement means for producing spacing movement in accordance with said output signal with consequent change in the magnitude of said first signal toward a coincidence with said second signal.

l0. A tabulating device for phototypesetting apparatus having character projecting mechanism and photosensitive material for recording the character images in sequence thereon, comprising means producing spacing movement between said projecting mechanism and said material according to the spacing requirements of each character used during composition of a line, means producing a Vfirst signal of variable magnitude related in magnitude to the space used while composing a line of given length, means for producing a second signal of variable magnitude related in magnitude to the spacing for a desired tabulating position, means comparing said signals and adapted to produce an output signal only when said first and second signals differin magnitude, and a tabulation spacing connection between the output -of .said 4comparingmeans .and said .spacing Amovement means for producing spacing movement in accordance with said output signal with consequent change in the magnitude of said rst signal toward a coincidence with said second signal.

11. A tabulating device for phototypesetting apparatus having character projecting mechanism and photosensitive material for recording the character images in sequence thereon, comprising means producing spacing movement between said projecting mechanism and said material according to the spacing requirements of each character and interword space used during composition of a line, means producing a rst variable signal related in magnitude to the space used while composing a line of given length, means producing a second variable signal related in magnitude to the space between the beginning of a line and a desired tabulating position spaced from the beginning, means comparing said signals and adapted to produce an output signal only when said rst and second signals dier in magnitude, and a tabulation spacing connection between the output of said comparing means and said spacing movement means for producing spacing movement in accordance with said output signal with consequent change in the magnitude of said rst signal toward a coincidence with said second signal, said spacing connection including a pulse generator controlled by said comparing means and operative to supply spacing information to said spacing movement means.

12. A tabulating device for phototypesetting apparatus having character projecting mechanism and photosensitive material for recording the character images in sequence thereon, comprising means for producing spacing movement between said projecting mechanism and said material according to the spacing requirements of each character used during composition of a line, said means including a space accumulating counter and a spacing transducer operated in correlation with said counter, means producing a lirst variable signal related in magnitude to the space used while composing a line of given length, means for producing a second variable signal related in magnitude to the space between the beginning of a line and a desired tabulating position spaced from the beginning, means comparing said signals and adapted to produce an output signal only when said rst and second signals diiTer in magnitude, and a tabulation spacing control controlled by the output signal from said comparing means and connected to operate said counter and said transducer for producing spacing movement with consequent change in the magnitude of said first signal toward a coincidence with said second signal.

References Cited in the file of this patent UNITED STATES PATENTS 2,714,843 Hooven Aug. 9, 1955 

